In a map database which a map processing system which is represented by, for example, a navigation device has, a plurality of types of map data having different scales, such as 1/2,500, 1/25,000, and 1/50,000, are stored. A navigation device mounted in a moving object selects a scale for a map to be displayed according to the travel speed of the moving object except when the user selects a scale for the map by using an operation button or a touch panel. More specifically, the navigation device detects the travel speed of the moving object, and, when this detected travel speed is equal to or lower than a predetermined speed A, selects a map scale X, when the travel speed is higher than the predetermined speed A and equal to or lower than a predetermined speed B, selects a map scale Y, or when the travel speed is higher than the predetermined speed B, selects a map scale Z. The navigation device then acquires map data for displaying the map having the selected scale from a map database, and creates display data according to this map data. This created display data is converted into a video signal, and this video signal is sent to a display unit. As a result, the map having the scale according to the travel speed is displayed on the screen of the display unit.
As an example of such a map processing system, patent reference 1 discloses a navigation device which displays a map of a surrounding area with a scale corresponding to the travel speed of a moving object. In this navigation device, a selecting means selects a map scale corresponding to the travel speed of the moving object which is detected by a speed detecting means, and an arithmetic processing means creates display data about a map image of an area surrounding the position of the moving object detected by a position detecting means with the scale selected by the selecting means on the basis of map data read from a map data storage means. A display control means reads the display data stored in a memory, converts the display data into a video signal, and causes a display means to display a map.